The present invention relates generally to an electron gun structure applied to a color cathode-ray tube apparatus, and more particularly to an in-line type electron gun structure wherein a cathode current can be made close to a predetermined value in a short time from the start of operation.
An in-line type electron gun structure applied to a color cathode-ray tube apparatus comprises three independent cathode structures, a first grid, a second grid and a third grid. The three cathode structures are horizontally arranged in the same plane. The first grid is disposed at a predetermined distance from the three cathode structures and controls three electron beams emitted from the three cathode structures. The second grid is disposed at a predetermined distance from the first grid and shields an electric field varying due to the first grid. The third grid is disposed at a predetermined distance from the second grid and accelerates the three electron beams which have passed through the second grid.
The cathode structure in the in-line type electron gun structure comprises a discoid cathode, a cylindrical cathode sleeve holding the discoid cathode, a cathode holder so formed as to surround the cathode sleeve and to serve as an envelope, and a thin, elongated plate-shaped cathode strap for coupling the cathode sleeve and the cathode holder. A heater for heating the cathode is disposed within the cathode sleeve.
The cathode sleeve is fixed by welding to the cathode strap. The cathode holder is fixed by welding to the cathode strap near a surface of the cathode holder, which is opposed to the first grid. Specifically, the cathode sleeve is fixed to the cathode holder by means of the cathode strap.
The cathode structure is held by a hold structure. The hold structure comprises a cylindrical cathode support cylinder for housing the cathode structure, and a cathode support strap for holding the cathode support cylinder. The cathode support strap is formed of an elongated plate having a cylindrically curved portion with a semicircular cross section. A cylindrical side surface of the cathode support cylinder is covered by, and fixed by welding to, the cylindrically curved portion of the cathode support strap. The length of the cylindrically curved portion in the direction of its generating line is slightly less than that of the side surface of the cathode support cylinder in the direction of its generating line.
The cathode structure is fixed by welding to the hold structure. Specifically, the cathode structure is fixed to the hold structure by welding the cathode holder of the cathode structure to the cathode support cylinder of the hold structure at predetermined weld positions. The weld positions for welding the cathode structure and hold structure are set on that area of the side surface of the cathode support cylinder, which is not covered by the cylindrically curved portion of the cathode support strap. In the hold structure with conventional structure, an area suitable for welding is only one near one end of the side surface of the cathode support cylinder, which is opposite to the first grid in the generating line direction.
In this in-line type electron gun structure, the cathode structures are so designed as to have the same cut-off voltage in order to obtain a good white screen image on the color cathode-ray tube apparatus. Specifically, the electron gun structure is designed such that the cathode current Ik supplied to each cathode structure has a predetermined constant value. However, in normal cases, the cut-off voltages of the respective cathode structures are not necessarily equal. Thus, in order to equalize the cut-off voltages, that is, in order to set the cathode current Ik at a predetermined constant value, a bias voltage is adjusted according to the characteristics of each cathode structure after the color cathode-ray tube apparatus was manufactured.
However, in this type of color cathode-ray tube apparatus, each cathode current Ik cannot be set at a predetermined constant value in a short warm-up time period. The warm-up time period begins when power is supplied to the heater and ends when the structural elements of the electron gun structure heated by the heater have reached the thermal equilibrium state, and it is in general about 20 minutes.
The reason for this is that there is a difference among the structural elements of the electron gun structure with respect to the time period from the switching-on of power to the heater until the structural elements of the electron gun have reached the thermal equilibrium state, and that a distance between a cathode surface of each cathode of the electron gun structure, which cathode surface is opposed to the first grid, and the first grid, that is, a G1/K gap, varies until the cathode current Ik stabilizes at a predetermined constant value.
More specifically, there is a great influence due to a difference in structure between the cathode structure disposed near the heater which directly produces heat, and the hold structure for holding the cathode structure. In other words, in an electron gun structure with grids to which predetermined voltages are applied, the cathode current Ik is determined mainly by the G1/K gap between the cathode surface of the cathode of the cathode structure and the first grid.
The structural elements disposed near the heater are heated and thermally deformed, if power is supplied to the heater. In this case, the heater itself first reaches the thermal equilibrium state and first reaches the stable state. The heater hardly affects the G1/K gap. The cathode strap having a small volume and a thin plate shape is the second to reach the thermal equilibrium state. Since the cathode strap reaches the thermal equilibrium state in a short time, thermal deformation progresses quickly. The cathode sleeve is the third to reach the thermal equilibrium state, and the cathode holder is the fourth.
Following the above, the cathode support cylinder, cathode support strap and first grid reach the thermal equilibrium state in the named order. The cathode support cylinder and cathode support strap have only negligible influence on the G1/k gap in the process of thermal deformation. The influence of the deformation of the first grid is also negligible, since beads or the like are formed around the grid or the plate-like electrode so as to prevent a change in position of the grid.
Thus, during the time period from the switching-on of power to the heater to the reaching to the thermal equilibrium state, the cathode current Ik is affected mainly by the difference in time needed for the cathode strap, cathode sleeve and cathode holder to reach the thermal equilibrium state, and the variation amount of the G1/K gap due to the thermal deformation of each structural element.
In the in-line type electron gun structure with the above-described construction, the time-basis variations of the value of cathode current Ik relative to the time from the switching-on of power to the heater may be separately considered according to the stabilization time periods of the respective structural components: a period A needed for the electron beam to be emitted from the cathode heated by the heater which was powered; a period B needed for the heated cathode strap to reach the thermal equilibrium state; a period C needed for the heated cathode sleeve to reach the thermal equilibrium state; and a period D needed for the heated cathode holder to reach the thermal equilibrium state.
About 20 minutes are needed until the structural elements reach the thermal equilibrium state completely, that is, until the cathode current Ik reaches a predetermined value. About 15 minutes are needed for the period E until the cathode current Ik reaches within a predetermined allowable range of the predetermined value Ik at which the stable state is substantially conformed in visual sense.
The problem with the variation of the cathode current Ik in the warm-up time period is that a considerable amount of time is required for the stabilization of the luminance and chromaticity of the screen when the color cathode-ray tube apparatus is activated. It is desirable that the stable state be quickly reached in visual sense and the period E be decreased.
As has been described above, the electron gun structure has the problem in that a great amount of time is needed from the activation, i.e. switching-on of power to the heater, until the cathode current stabilizes within a predetermined allowable range of values. In the color cathode-ray tube apparatus using the electron gun structure, the warm-up time will increase for achieving predetermined screen luminance and predetermined chromaticity.
The present invention has been made to solve the above problems, and its object is to provide an electron gun structure applicable to a color cathode-ray tube, which is capable of shortening the warm-up time, and obtaining in a short time luminance and chromaticity of predetermined levels without significant difference in visual sense.
According to the present invention, there is provided an electron gun structure comprising:
a cathode structure including a cathode;
a heater for heating the cathode;
a hold structure including a cathode support cylinder in which the cathode structure is inserted and held, and a cathode support strap having an elongated plate shape and having an engagement surface engaging a side surface of the cathode support cylinder;
a grid disposed to be opposed to the cathode; and
insulative glass in which a part of the hold structure and a part of the grid are embedded and fixed,
wherein the cathode support strap has at least one opening portion formed in a part of the engagement surface, and
the cathode structure and the cathode support cylinder are welded through the opening portion and fixed.
According to the electron gun structure of the present invention, the elongated plate-shaped cathode support strap has the opening portion at least in a part of the engagement surface engaging the cathode support cylinder. The cathode support cylinder and the cathode structure are welded through the opening portion and fixed.
Thus, although the time needed for each structural element of the cathode structure and hold structure to reach the thermal equilibrium state is unchanged, the weld position between the cathode structure and the cathode support cylinder can be made closer to the grid and accordingly the thermal deformation amount of each structural element, which may affect the variation of the gap between the cathode and the grid, can be greatly reduced.
More specifically, although the time needed to reach the thermal equilibrium state is unchanged, the state which has no significant difference from the thermal equilibrium state in visual sense can be quickly reached. Therefore, the warm-up time from the activation can be decreased.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.